The present invention relates to complexes of 2,6-pyridinebis(imines) with transition metals and their use for polymerizing alpha-olefins.
It is known that alpha-olefins can be polymerized by means of complexes comprising a transition metal and a tridentate ligand, and an aluminoxane. Patent application WO 99/62967 describes the copolymerization of ethylene with the aid of complexes of iron with 2,6-pyridinebis(imines). However, the catalytic complexes described in that application do not efficiently incorporate propylene during the manufacture of copolymers of ethylene. Patent application WO 99/12981, Britovsek et al. (Chem. Eur., 2000, 6(12), 2221) and Qiu et al. (Polym. Int., 2000, 49(1), 5) report the syntheses of {2,6-bis[1-(1-naphthylimino)methyl]-pyridine-xcexa3: N,Nxe2x80x2,Nxe2x80x3}FeCl2 and of {2,6-bis[1-(1-naphthylimino)ethyl]pyridine-xcexa3: N,Nxe2x80x2,Nxe2x80x3}FeCl2 and their use for polymerizing ethylene in the presence of methylaluminoxane (MAO). However, the catalytic activity of these complexes and the molecular weights of the polyethylenes obtained are low.
We have now found complexes of a transition metal with 2,6-pyridinebis(imines) for polymerizing alpha-olefins where these do not have the abovementioned disadvantages.
The present invention therefore provides complexes of a transition metal complying with the general formula (I) in which 
M is a transition metal of groups 6 to 12,
T is the oxidation state of M,
each A, which may be identical with or differ from each other, is an atom or an atomic grouping bonded covalently or ionically to the transition metal M,
b is the valency of A,
each R1, R2, R3, R4 and R5 is independently a hydrogen atom, an unsubstituted or substituted hydrocarbon group, an unsubstituted or substituted heterohydrocarbon group, or an inert functional group,
R6 and R7 are, independently of one another, a polynuclear aromatic hydrocarbon group containing at least two condensed benzene nuclei, substituted with at least one hydrocarbon group.
All the references to the Periodic Table of the Elements refer to the version published in CRC Handbook of Chemistry and Physics, 77th Edition, 1996/97; the notation utilized is the new IUPAC notation for the groups.
An xe2x80x9cinert functional groupxe2x80x9d is understood to be an atomic grouping which is not an unsubstituted or substituted (hetero) hydrocarbon group, this group being inert under the conditions of the process using the complex of the present invention, and not coordinating with the transition metal M. Examples which may be mentioned of inert functional groups are halogen atoms and ethers of formula OR in which R is an unsubstituted or substituted hydrocarbon group.
Preferred complexes are those complying with the general formula (I) in which M is Fe, Cr, Co, Ru or Mn. Particular preference is given to Fe. Suitable complexes are those complying with the general formula (I) in which T is 2.
Each A is generally selected from halogen atoms, sulphates, nitrates, thiolates, thiocarboxylates, BF4xe2x80x94, PF6xe2x80x94, hydrogen atoms, hydrocarbon oxides, carboxylates, unsubstituted or substituted hydrocarbon groups, and heterohydrocarbon groups. Preferred complexes are those complying with the general formula (I) in which A is a halogen atom or a linear or branched alkyl group containing from 1 to 8 carbon atoms. Preference is very particularly given to complexes of the formula (I) in which A is a halogen atom.
Suitable complexes of the invention are those complying with the general formula (I) in which R1, R2, R3, R4 and R5 are independently a hydrogen atom or a linear or branched alkyl group containing from 1 to 6 carbon atoms. The complexes in which R1 and R5 are independently a linear or branched alkyl group containing from 1 to 6 carbon atoms are particularly preferred, since they have high activity.
R6 and R7 are preferably selected independently of each other from groups complying with the formulae (II) or (III) below: in which R8 to R21 are independently hydrogen atoms or hydrocarbon groups, such 
that at least two thereof can form a ring, with the proviso that at least one of the groups selected from R8 to R14 is not a hydrogen atom.
The groups (II) in which R11 and R12, R12 and R13, or R13 and R14 together form an unsubstituted or substituted benzene nucleus advantageously give alpha-olefin polymers having high molecular weight. The groups (II) in which R12 and R13 together form an unsubstituted or substituted benzene nucleus are particularly suitable. The groups (II) in which at least one of the groups selected from R12, R8 and R9 represents a linear or branched alkyl group containing from 1 to 8 carbon atoms are preferred because they generally give high catalytic activity. The groups (II) in which R8 is a linear or branched alkyl group containing from 1 to 8 carbon atoms are particularly preferred. The groups (II) in which R12 and R13 together form an unsubstituted or substituted benzene nucleus and R8 is a linear or branched alkyl group containing from 1 to 8 carbon atoms are particularly preferred because they usually permit alpha-olefin polymers having high molecular weight to be obtained with high activity.
The groups (III) in which R18 and R19, R19 and R20, or R20 and R21 together form an unsubstituted or substituted benzene nucleus usually give alpha-olefin polymers having high molecular weight. The groups (III) in which at least one of the groups selected from R15 and R16 is a linear or branched alkyl group containing from 1 to 8 carbon atoms are preferred because they generally give complexes having high catalytic activity. The groups (III) in which R19 and R20 together form an unsubstituted or substituted benzene nucleus and R15 or R16 is a linear or branched alkyl group containing from 1 to 8 carbon atoms advantageously permit alpha-olefin polymers having high molecular weight to be obtained with high activity.
It is preferable to use complexes in which R6 and R7 comply with formula (II). The complexes in which R1 and R5 are a linear or branched alkyl group containing from 1 to 6 carbon atoms, and R6 and R7 comply with the formula (II) in which R8 is a linear or branched alkyl group containing from 1 to 8 carbon atoms are very particularly preferred. Examples which may be mentioned of abovementioned complexes are {2,6-bis[1-(2-methyl-1-naphthylimino)methyl]pyridine-xcexa3: N,Nxe2x80x2,Nxe2x80x3}FeCl2, {2,6-bis[1-(1-anthracenylimino)methyl]pyridine-xcexa3: N,Nxe2x80x2,Nxe2x80x3}xe2x80x94FeCl2, {2,6-bis[1-(1-anthracenylimino)ethyl]pyridine-xcexa3: N,Nxe2x80x2,Nxe2x80x3}FeCl2 and {2,6-bis[1-(2-methyl-1-naphthyl-imino)ethyl]pyridine-xcexa3: N,Nxe2x80x2,Nxe2x80x3}FeCl2.
The complexes of the invention are generally prepared by a first condensation step of Schiff-base type, using amine and unsubstituted or substituted 2,6-bis(carbonyl)pyridine, as described by Britovsek et al. in J. Am. Chem. Soc., 1999, 121, 8728 and Small et al. in J. Am. Chem. Soc., 1998, 120, 4049. This reaction is then followed by addition of the di(imino)pyridine thus obtained to a salt of the transition metal (M) in order to obtain a complex complying with the general formula (I). The condensation reaction is usually carried out by using 2 equivalents of amine to 1 equivalent of 2,6-bis(carbonyl)pyridine. The di(imino)pyridine obtained is preferably added to a halide of the transition metal (M). This complexation reaction may be followed by reaction of the complex obtained with a Grignard reagent of formula AMgBr, in which A is a linear or branched alkyl group containing from 1 to 8 carbon atoms.
The complexes of the invention may be used as catalysts for polymerizing alpha-olefins. The invention therefore also provides a process for polymerizing alpha-olefins by bringing at least one alpha-olefin into contact, under polymerizing conditions, with a catalytic system comprising
(a) a complex of a transition metal from groups 6 to 12 in accordance with the invention and
(b) at least one activator.
The activators are generally selected from organoaluminium compounds. Use is usually made of aluminoxanes or of trialkylaluminium compounds. The preferred aluminoxane is methylaluminoxane (MAO). The trialkylaluminium compounds are advantageously selected from trimethylaluminium (TMA), triethylaluminium (TEA), triisobutylaluminium (TIBAL), and mixtures of these.
The quantity of activator used in the process of the invention is generally such that the atomic ratio of aluminium to the transition metal (M) derived from the complex (a) is from 10 to 20 000. This ratio is preferably at least 30, more particularly at least 50. Good results are obtained when this ratio is at least 100. This ratio is usually not more than 10 000. Ratios of from about 200 to 6000 give particularly good results.
For the purposes of the present invention, alpha-olefins are understood to be terminally unsaturated olefins generally containing from 2 to 20 carbon atoms, preferably from 2 to 8 carbon atoms. Examples of alpha-olefins are ethylene, propylene, 1-butene, 1-pentene, 1-hexene and 1-octene. Besides the olefin, it is of course possible for another monomer copolymerizable with the olefin to be used in the process of the invention.
The polymerization process of the invention may be carried out continuously or batchwise, in accordance with any known process, in solution, or in suspension, or even in the gas phase. The polymerization process of the invention is advantageously carried out in suspension in the monomer or in one of the monomers, kept in the liquid state, or in a hydrocarbon diluent, generally selected from aliphatic hydrocarbons containing from 3 to 10 carbon atoms. The diluent is preferably selected from propane, isobutane, hexane, and mixtures of these.
In the process of the invention, the complex of the transition metal (a) is preferably mixed with the activator (b) before it comes into contact with the alpha-olefin. In one advantageous version of the process of the invention, only some of the activator may be used for mixing with the complex, the rest of the activator being introduced directly into the polymerization reactor, optionally in the presence of alpha-olefin. The quantity of activator used in precontact is generally such that the atomic ratio of the aluminium to the transition metal (M) derived from the catalytic complex (a) is from 1 to 10000. This ratio is preferably at least 10, more particularly at least 50. Good results are obtained when this ratio is at least 100. The quantity of activator is usually such that this ratio is not more than 5000. Ratios of from about 300 to 2000 give particularly good results.
The temperature at which the polymerization is carried out is generally from xe2x88x9220 to +150xc2x0 C., typically from 20 to 115xc2x0 C.
The total pressure at which the process of the invention is carried out is generally selected between atmospheric pressure and 100xc3x97105 Pa, more particularly between 5xc3x97105 and 55xc3x97105 Pa.
The polymerization process of the invention is advantageously applied to the manufacture of polymers of ethylene, and more particularly to the manufacture of homo- and copolymers of ethylene. Homopolymers of ethylene thus frequently have ethyl and/or butyl branching. The preferred copolymers are those of ethylene with another alpha-olefin containing from 3 to 8 carbon atoms. Particular preference is given to copolymers of ethylene with propylene, with 1-butene and/or with 1-hexene. In the case of copolymerization of ethylene with another alpha-olefin containing from 3 to 8 carbon atoms, the polymerization is preferably carried out in that alpha-olefin in the liquid state, and with a low concentration of ethylene, based on the concentration of alpha-olefin, in the polymerization medium.
The process of the invention can give alpha-olefin polymers with high catalytic activity and can manufacture alpha-olefin polymers of high molecular weight. It can also give branched polyethylenes, or copolymers of ethylene, and more particularly copolymers of ethylene which may contain up to 99% by weight of monomeric units derived from propylene. These polymers are therefore a supplementary subject-matter of the present invention.